Forget your umbrellas -- in this game, the whole point is to get soaked.
Provide each team with one empty and one full bucket, as well as a plastic cup.
Set the empty buckets at one end of the yard and the full ones at the other near the kids.
At the word "Go," the first player on each team dips his cup into his water bucket and holds it over his head as he dashes to the other end of the yard. (No covering holes with fingers, please!)
When a player reaches the second bucket, he dumps what's left in his cup into it, runs back to the start, and passes the cup to the next player.
The game continues until the formerly full bucket is empty.
The team with the most water in the second bucket wins.